Method of transmitting half tone pictures by telegraph



Aug. 10, 1937.

o. SCH RIEVER 2,089,667

METHOD OF TRANSMITTING HALF TONE PICTURES BY TELEGRAPH Emu Patented Aug. 10, 1937 OFFICE METHOD OF TRANSMITTING HALF TONE PICTURES BY TELEGRAPH Otto Schriever, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose 'li'elegraphic in. b. H., Berlin, Germany, a corporation of Germany Application January 26, 1932, Serial No. 588,957 In Germany January 30, 1931 3 Claims.

In picture telegraphy the transmission of halftone pictures is attended with certain dimculties compared with simple black-White contrast pictures. By the aid of the so-called time-modula- 5 tion principle an attempt has therefore been made to insure and produce the different shades by telegraphic impulses of the same intensity though different length of time. However, inasmuch as each transmission channel usually has an impulse limit which is attempted to be reached in black-white contrast pictures, the said method is attended with an extension of the transmission time in the same measure as degrees of shading are to be re-created. t

This inconvenience is obviated by the present invention which consists in transmitting the continuous range of shading from black to white by gradations upon a plurality of transmitting channels each one of which may be utilized by the picture signals or impulses up to the extremest impulse limit.

Themany objects of the invention will at once become apparent and suggest themselves to those skilled in the art to which the invention is directed by referring to the accompanying drawing I basic principles of the invention;

Fig. 2 illustrates one embodiment of the invention; and

Fig. 3 shows the use of a perforated disk to produce alternating current effects when combined with a system such as has been shown by Fig. 2,

To refer now to the drawing: The picture current by the agency of an amplitude-depending ele- M ment A, in accordance to its momentary intensity,

is brought to act upon one of the relays R (preferably of the hot or photo-electron relay type).

The particular relay which is thus acted upon causes, in turn, the channel K coordinated thereto to be rendered operative during the period that this relay operates. Thus, in black channel I 5 might operate, whereas for white channel IV would be operative.

The embodiment of the invention shown by way of example in Fig. 2 is a practical means of utilizing the principle shown by Fig. 1. Referring now to Fig. 2 of the drawing, i denotes an oscillograph mirror actuated by the photo-current, 2 is a system of rectangularly cut-out condensing lenses of the illuminated slit 3 over which the light reflected from the mirror is caused to sweep. The light impinging upon the lenses 2 is focussed in the foci l, l, 4" thereof. According to the deflection of the mirror, one of the said foci will be caused to flash up with the result that, by the aid of the coordinated photo-electric cell 5, 5', or 5" the corresponding telegraphing channel 6, 6, or 6" is rendered operative.

For reasons associated with the amplifiers it is of advantage to obtain the photo-electric currents in the form of A. C. impulses rather than in the shape of D. C. impulses. According to this invention, as shown in Fig. 3, this result may be attained by the use of a revolving perforated disk 1 having several circles of holes 8, 8' and 8" of varying number disposed that each of the different foci comes to be placed upon another row of holes and as the disk is rotated the light to v the photocells will be correspondingly interrupted.

According to the amplitude of the mirror, i. e., according to the brightness of the picture spot that happens to be scanned at the time, there will be obtained from the photo-electric cell which happens to respond an A. C. having a frequency characteristic of the brightness or shading degree in question; and the amplification of this current is no longer attended with any diificulties contradistinct from what is true of the amplification of pure D. C. impulses.

For the sake of further simplification of this scheme, it is possible to use beyond the perforated disk for all of the channels a joint photoelectric cell and a joint amplifier, the shading differences being restored again above the amplifier by suitable filter circuits.

It will be understood that in lieu of a single perforated disk also a plurality of such disks could be used, though it will also be evident that any other ways and means of light-ray modulation such as a vibratory tuning fork to intercept the light or a supply of A. C. of diiferent frequency to each photocell or equivalent schemes could be employed.

As regards the nature of the channels to be employedwhen working with wire transmission it will be preferable to send the tones thus obtained directly over the existing wire connection. In the case of wireless work a similar procedure could be adopted in that a joint carrier Wave is used for the alternatively arising tones. To be sure when using tones care must be taken so that.

the overtones of one of the channels will not get into the channel of another tone as this would result in a scrambling of the picture shades or tones. Especially in short-wave work it may easily happen that overtones come in with greater volume than the fundamentals.

In caseof a low number of tones cross-talk may be fairly precluded by the suitable selection of the tonal frequencies. But if, with a view to insure better picture quality the number of the 5 channels is allowed to be greater, the said dimculty becomes practically insurmountable. Hence, it is of greater practical advantage to avoid the transmission of characteristic tones and to use these at the sending end according to requisite amplification and optional separation, according to this invention in this manner that a plurality of carrier waves suitably spaced apart are alternately modulated Whether in this case tone modulation is to be preserved or whether the 1 carrier waves should be modulated by D. 0. im-

pulses is a question that depends solely upon the general conditions of transmission, and this has nothing to do with the half-tone character of the transmitted picture.

The separation and final re-combination of the various'channel's at the receiver end for the object of insuring a proper re-creation of the picture is insured by ways and means well known in the prior art.

I claim:

1. In a system for transmitting picture records or the like, the method which comprises analyzing successive elemental areas of ,a picture record in accordance with the varying intensities of light and shadow of successive elemental areas thereof to produce proportionately varying electrlc current impulses, controlling an oscillograph in accordance with the varying intensity electric current impulses, producing light of substantially constant intensity and directing the produced light along a predetermined path, influencing separate light sensitive bodies by the constant intensity light in accordance with difi'erent deflections in the controlled oscillograph produced by difierent intensity electric current impulses, producing an output current from each light sen sitive body of substantially constant intensity at time periods when the body is subjected to the constant intensity light, introducing into each separate image signal current a tone frequency of diiferent related values and combining all of said signals for transmitting a record representative of the varying intensities of light and shadow on successive elemental areas of the record subject.

2. In a system for transmitting electro-optical images of a. record subject, means for converting successive elemental areasof a record subject into proportionately varying electric current impulses, means for producing a steady source of light and projecting said light across a predetermined path, a plurality of light translating elements of a number equal to the number of gradations of shade into which the picture subject is to be divided, means responsive to tne varying intensity current impulses for activating successively said plurality of light translating elements, means for introducing into each of said light translating elements a separate and distinct tone frequency whereby the varying intensities of light and shadow are converted from amplitude modulated sig nals into frequency modulated signals, and means for transmitting said frequency modulated signals. V 3. The method of transmitting pictures which comprises resolving the subject of which an electro-optical representation is desired into a series of discrete shade values and transmitting for each shade value a difierent carrier frequency signal each of said carrier frequency signals being of substantially equal amplitude.

'o'r'ro SCl-IRIEVER. 

